Tall oil pitch is obtained as a distillation residue of the conversion of crude tall oil. In Finland, the tall oil distilling plants produce about 20,000 tons of tall oil pitch annually.
This tall oil pitch may be used for various purposes. Its main use is for burning, the tall oil pitch being mixed with fuel oil and burned in power plants.
Tall oil pitch contains resins and fatty acids of the crude tall oil and unsaponifiable components. The resins and fatty acids of tall oil pitch react with calcium oxide which neutralizes the tall oil pitch and forms calcium soaps as a reaction product.
Tall oil pitch is characterized by the following: softening point (in .degree.C.), acid number (in mg KOH per g) and the saponification number. The amount of calcium oxide required to neutralize the tall oil pitch is calculated from the acid number.
Literature in the field has described the manufacture of binding agents for coatings from tall oil pitch in which the esters have been modified with maleic anhydride ("Tall Oil and its Uses", L. G. Zachary, H. W. Bajak and F. J. Eveline, McGraw-Hill Inc., New York, 1965, page 50). There is therein described a process wherein polyol esters of tall oil pitch are modified with maleic anhydride. This thus neutralized tall oil pitch has a high acid number, and softening point of 100.degree.-110.degree. C.
This process carries with it several technical drawbacks. In the first place, the high energy consumption and the use of protective gas are factors which exert an unfavorable effect on the overall manufacturing costs. Secondly, the preparation of the solution requires a separate process, thus further increasing the costs. Still further, we have found that the preparation of the solution is further impeded by the formation of a gel in the case of high solid matter content. We have still further found that the high acid number of the coatings thus produced can cause corrosion on a metal base, and a coating of this kind therefore cannot properly be used as anti-rust agent for anti-rust compositions.
There is a distinct difference between tall oil and tall oil pitch. Tall oil pitch is a distillation residue obtained during the conversion of tall oil. Tall oil pitch is a pitch-like product which is totally different from oily tall oil in its chemical structure and consistency.
The criteria commonly employed in quality specification of tall oil products are the acid number and the saponification number. The following characteristic values have been reported for commercial tall oil (cf. "Tall Oil 108"):
Acid number, mg KOH per g: 189-194 PA1 Saponification number mg KOH per g: 193 PA1 Fatty acids %: 86-92 PA1 Resin acids %: 6-10 PA1 Unsaponifiable %: 2-4 PA1 Acid number mg KOH per g: 27-49 PA1 Saponification number mg KOH per g: 94-115 PA1 Free acids, %: 34,6-51,6 PA1 Esterified acids, %: 23,2-37,8 PA1 Unsaponifiable %: 25,3-30,1
According to the studies (cf. "Composition of Tall Oil Pitch"), tall oil pitch can be characterized on the basis of the following characteristic values:
As the above figures reveal, there is a substantial difference between tall oil and tall oil pitch. The differences between these products are clearly apparent, not only in the acid and saponification numbers, but also in chemical composition. Tall oil pitch is characterized by high contents of esterified acids and of unsaponifiable fraction. Tall oil, on the other hand, contains mainly fatty acids and no esterified acids at all.
U.S. Pat. No. 3,128,195 to A. Patellis relates to a method of making limed tall oil in which calcium oxide is used to neutralize a mixture of mineral oil, crude tall oil and tall oil pitch (26%). The acid number of the neutralized mixture is 8.2 and this mixture is used as a cement for fixing flooring tiles.